1. Field of the Invention
This invention relates to a novel catalyst, to the production thereof and to the use thereof for the polymerisation of conjugated dienes, in particular butadiene, in the gas phase.
2. Description of the Prior Art
Polybutadiene with an elevated proportion of cis-1,4 units has long been produced on a large industrial scale and used for the production of tires and other rubber articles. Polymerisation is performed in this connection in the liquid phase using the most various catalyst systems. A particularly advantageous catalyst system for the production of polybutadiene with an elevated proportion of cis-1,4 units is described in European Patent 11 184. The catalyst system which is described therein and used for solution polymerisation of butadiene consists of a rare earth carboxylate, an aluminiumtrialkyl and/or alkylaluminium hydride and a further Lewis acid.
Polymerising conjugated dienes in solution has the disadvantage that when the unreacted monomer and the solvent are separated from the formed polymer, low molecular weight compounds may escape to the environment in exhaust air and effluent and must thus be appropriately disposed of.
It is also known (EP 201 979) to polymerise conjugated dienes without adding solvents in the liquid monomers. However, such a process has the disadvantage that a large quantity of heat is liberated on complete polymerisation, which is difficult to control and thus constitutes a certain potential hazard. Moreover, here too, there is an environmental impact when the polymers are separated from the monomers.
In recent years, the gas phase process has proved particularly advantageous, particularly for the production of polyethylene and polypropylene and has become widely used industrially. The environmental advantages of the gas phase process are in particular that no solvents are used and emissions and effluent contamination may be reduced.
There has hitherto been no known process for the direct gas phase polymerisation of conjugated dienes, in particular of butadiene. One reason for this may be that the Ziegler-Natta catalysts based on titanium, cobalt, nickel or neodymium which are used for the solution polymerisation of conjugated dienes are not straightforwardly suitable for gas phase polymerisation, in particular due to their low productivity, i.e. the small quantity of polymer which may be produced with a certain quantity of catalyst. Thus, due to its rapidly falling activity when used in gas phase polymerisation, the catalyst described in EP 11 184 is virtually completely unsuitable to polymerise conjugated dienes, in particular butadiene, in the gas phase to yield polymers with an elevated proportion of cis-1,4 units (see comparative test).
German Application P 43 34 045.8 contains the first description of a catalyst system which allows the polymerisation of conjugated dienes, in particular butadiene. The catalysts described in the stated application consist of rare earth compounds and an inorganic support.
The object of the present invention was thus to provide novel catalysts for the polymerisation of conjugated dienes, in particular butadiene, from the gas phase, which catalysts may advantageously be used in the gas phase process.
It has now surprisingly been found that it is possible to polymerise conjugated dienes, in particular butadiene to yield polybutadiene, with an elevated cis-1,4 double bond content, from the gas phase with rare earth catalysts if certain rare earth allyl compounds in combination with an aluminiumalkyl and an inorganic support are used.
The present invention thus provides a catalyst consisting of:
A) a rare earth allyl compound of the formula (I) EQU (C.sub.3 R.sub.5).sub.n MX.sub.3-n' (I), PA1 in which PA1 B) an organoaluminium compound selected from the group comprising aluminiumtrialkyls (II), dialkylaluminium hydrides (III), dialkylaluminium halides (IV) or alkylaluminium dihalides (V) and/or an alumoxane of the formulae (VI) to (VII): EQU AlR'.sub.3 (II), HAlR'.sub.2 (III), R'.sub.2 AlX (IV), R'AlX.sub.2 (V), R'.sub.2 AlOAl(R')!.sub.n OAlR'.sub.2 (VI), OAlR'!.sub.n-2(VII), PA1 wherein, in the formulae, PA1 C) an inert, particulate, inorganic solid with a specific surface area of greater than 10 m.sup.2 /g (BET method) and a pore volume of 0.3 to 15 ml/g, and optionally PA1 D) a conjugated diene.
M means a trivalent rare earth element with an atomic number of 57 to 71, PA2 X denotes Cl, Br, I, NR.sub.2, OR, RCO.sub.2, C.sub.5 H.sub.m R.sub.5-m, C.sub.5 H.sub.m (SiR.sub.3).sub.5-m, C.sub.1 to C.sub.6 alkyl, (C.sub.6 H.sub.5).sub.3 C, RS, N(Si(CH.sub.3).sub.3).sub.2 with R having the following meaning, PA2 R is identical or different and means hydrogen or an alkyl, aralkyl or aryl group with 1 to 10 carbon atoms, PA2 n' is 1 to 3, and m is 1 to 5, PA2 R' is identical or different and means an alkyl group with 1 to 12 carbon atoms, PA2 X is Cl, Br, I, or OR', and PA2 n means 1 to 50, except where the alumoxane of the formula (VII) is cyclic, in which case n is at least about 6,